OVERVIEW: What every practitioner needs to know

Baylisascariasis in humans is caused by infection with the raccoon roundworm, Baylisascaris procyonis. This parasite causes severe or fatal encephalitis (neural larval migrans), most often in infants and young children. It usually manifests as an eosinophilic meningoencephalitis.

Humans become infected by ingesting soil, woodchips, or other material contaminated with raccoon feces containing B. procyonis eggs. Pica and geophagia are risk factors. Not only raccoons but also kinkajous, coatis, and other procyonids can harbor this roundworm.

Most of the limited number of reported human cases have occurred in boys, who present with an acute fulminant eosinophilic meningoencephalitis, with fever, ataxia, progressive lethargy, irritability, and somnolence. Ultimately, loss of milestones and regression develop, leading to posturing, spasticity, paresis, seizures, and ocular or cranial nerve involvement. Mortality is high, and survivors almost always are severely disabled.

What are the adverse effects associated with each treatment option?

Prognosis is very poor with or without treatment. The usual therapy includes antihelminthic agents plus steroids. Thiabendazole, fenbendazole, tetramisole, and ivermectin have been used, but albendazole is favored because of its excellent CSF penetration and larvicidal activity.

What are the possible outcomes of Baylisascaris procyonis?

Up to one half of affected patients may die. All reported survivors except one were left with very significant neurologic sequelae.

How does this pathogen cause disease?

Ingestion of B. procyonis eggs by young humans with pica or geophagia leads to hatching of the eggs in the gut. The larvae penetrate the gut wall and migrate to the brain (as well as to eye or viscera). Migration of larvae through the brain (neural larval migrans) causes tissue damage, leading to granulomas, eosinophilic inflammation, and necrosis.

Other Clinical Manifestations

Ocular larval migrans also can result from B. procyonis, either in isolation or with severe neural larval migrans. This can lead to visual impairment or blindness. Chorioretinitis, optic neuritis, or atrophy can result.

How can Baylisascaris procyonis be prevented?

Prevention of this devastating infection involves (1) educating the public regarding the dangers of contact with raccoons and their feces, (2) discouraging pica in young children, (3) handwashing after outdoor play or animal contact, (4) discouraging raccoon visitors or pets, (5) decontaminating raccoon latrines, and (6) avoiding feeding raccoons.